High frequency amplifier system



Aug. 10,v 1937. F. A. KoLsTER 2,089,270

HIGH.FREQUENCY AMPLIFIER SYSTEM Original Filed Feb. 2, 1925 L5 LL6 iece'iver:

Patented Aug. 10, 1937 HIGH FREQUENCY AMPLIFIER SYSTEM Frederick A. Kolster, New York, N. Y., assignoi' to Federal Telegraph Company, San Francisco,

Calif.,a corporation of California, y

Application February 2, 1925, Serial No. 6,259 Renewed June 1, 1932 4 claims". l (ci. 179-171) This invention relates to a system for amplifying high frequency electrical energy, and especially to a radio frequency` system employing electronic emission amplifier tubes.

Such radio frequency systems are in quite general use in connection with broadcast receivers, in which there may be one or more stages of radio frequency amplification. It has been found that in such systems, the eciency varies with the frequency. Since the present broadcast-range of from 200 to 550 meters corresponds to a variation in frequency 'between 546 kilocycles and 1500 kjlocycles, it is seen that even for this broadcast range, material variation in the efficiency of the amplifier can be expected unless some means be employed to render the operation more uniform. It is one of the objects of my invention to 'make it possible to operate the amplifier at substantially the same eiciency independently of this frequency variation.

It is another object of my invention so to arrange matters. in such a system that no adjustment is necessary to secure this beneficial effect, after the broadcast receiver is once placed into operation.

I It is still another object of my invention to provide a system of amplification in which lthe currents vflowing in the Aoutput circuits of the successive stages may be controlled automatically to cause substantially similar amplifying. effects independently of frequency variations.

My invention possesses other advantageous features, someof which` with the foregoing, will be set forth at length in the following description, where I shall outline in full that form of the invention which I have selected for illustration in the drawing accompanying and forming part of the present specification. Although I have shown in the drawing but one embodiment of my invention, I do not desire to be limited thereto, since the invention as defined in the claims may be embodied in other forms also.

Referring tothe drawing:

Figure 1 is a wiring diagram of a broadcast receiver and amplifier embodying my invention; y

and

Fig. 2 shows curves for explaining the'operation of the system disclosed in Fig. l.

In Fig. 1 the system is shown as applied to an amplifier system of two stages, each stage having.

a three-electrode electron emission tube I I or I2; but of course the invention may be embodied in a -system having less or a greater number of stages. The first tube Il has an output circuit consisting-of the control electrode I3 and an` 5 electron emitting electrode I4, connected to a circuit I5 which is arrangedlto carry the electrical currents or impulses to be amplified. In the case of ,a broadcast receiver, circuit I5 is usually a circuit tuned to the frequency of reception as by the condenser I6, and coupled to any appropriate source of signal energy. `rI'he electron emittingelectrode I4 is in this instance y in the form of a filament heated by current supplied froin a battery or other source I'I. x 15 The output circuit in which the ampliiied'impulses or currents flow, is connected between the plate or anode I8 and the filament I4, the space between these two electrodes being bridged by the ow of electrons from filament I4. Since the operation of such amplifiers is now wellknown, it is suicient at this point to state that the output circuit of such devices must include a source of direct current voltage, such as a battery I9,to impress a positive potential on plate 25 or anode I8 as regards the filament I4.

In most radio frequency amplifiers as heretofore constructed, the circuits are inductively coupled together so that the amount of current passed by the coupling arrangement will increase with an increase in frequency, as the impedance of an inductance is a function of the frequency of the current, and no attempt has been made to compensate for the fact that this current is a function of the frequency of operation, Whereby greater transfer of energy is obtained for high frequencies than at low frequencies. I overcome this disadvantage by so larranging the output circuit that the value of that portion of the current affecting the succeeding stage or the detector, no longer varies materially for different frequencies within a given range, even if the total output current varies. To accomplish this result, I use two impedance branches or paths for the output current, and the current flowing in one of these branches is controllable as desired, by the proper choice of constants. Thisbranch comprises 'a condenser Ci and an inductance Li in series, While the other branch consists of an nductance L2. It can be shown that by proper 2 choice of values of L1, c1 and L1, the division of current in the two branches lcan be made to vary with the frequency. To understand how this is accomplished, attention is now directed to Fig. 2.

tively to 546fkilocycles, and to 1500 kilocycles. i'

A calculation according to well-known formulae, of the reactance of branchC1 L1 will produce .a curve of-the form shown 4at either 22 or 23 depending upon the relative absolute values of capac'itance and inductance. plotted from the formula It is evident that when thefrequency ,f approacheszero, the value of reactance X1 increases negatively without limit. This is shown in Fig. 2

by making curves`22 and 23 asymptotic as regards the vertical line 2d passing through the origin. On the other hand, for large values of f, the reactance-X1 is positive. By proper choice of the values of C1 and L1, it is possible to vary the slope of the curve, and to make it have positive ordinates at or near the 546 kilocycle line 20. The curve 23 is similar to curve 22 ex- These curves are cept for a different ratio o f'C1'and L1, the curvel 23 being steeper. Preferably the constants are ,such that the reactance reduces to zero (correk spending to a tuned condition) at a frequency just a little below the lower limit of operation, or

below 546 kilocycles.

The total reactance impedance X of the output circuit, or of the two branches in parallel will be4 Therefore it is evident` that as the system is tuned to different frequencies, the totalreactance will increase with increased frequencies.

The inductance L2 forming the second branch ispreferably chosen so as to make its reactance about equalto that of the other path at or near I the higher limit of frequency. 4This is shown by the curves 25 and 26, corresponding respectively with the curves 22 and 23. These curves are in fact straight lines passing through the origin,

for they obey the law that to permit the ow of direct current in the output circuit. But' the radio frequency amplied current has two paths, and divides between them. .At

the high frequency limit, the radiov frequency current is preferably about evenly divided be-" coil La, whereby the current in' coil L1 is the only .factor affecting this succeeding stage. The

75 scheme of connection-forthis stage need not-be aosaavo In is available described in detail, for itis substantially similar tothat already described. The input circuit of tube I2 is connected across the tuning condenser '21 which is in a closed circuit with coil Ls whereby the input circuit may be selectively tuned to any frequency `within a given rangeA of radio frequencies; and its output circuit also includes the two branch circuits L4, and C5-L5. The proportions'of the elements L4, C5, and Lsare determined as before.

Still further stages may be employedgas desired, similarly constructed. However, since the principle wouldbe exactly the same as before, I show only the two stages, and indicate a receiver 28 as coupled by the aid of coil Le to the coil La.

The coupling between coils L1 and La and be' tween coils Ls and Ls is somewhat critical, but

when once the proper value is "found, the amplifler system operates properly and without requiring other attention.

The'manner o f operation of the sys-tem is evident from the foregoing description. The condensers i6, 21, and 29 are adjusted to selectively tune the stages to the frequency of operation. Due to the choice of constants as explained, the efficiency of the amplifier system remains substantially unaltered without making coupling adjustments no matter what the frequency of operation may be.'

I claim:` 1. In an amplier system for amplifying electrical impulses of radio-frequency the frequency of which may vary between limits, an electronic emission tube, andan output circuit for said tube comprising a pair of parallel paths, one consisting substantially entirely of inductance, and the other of an inductance and a capacity in series, said two paths being so arranged that at the high frequency limitof operation'the reactances of both paths are substantially equal, and at the low frequency limit, both have positive reactances but of differing values, and a selectively tuned circuit coupled to the inductance in said second parallel path whereby thecurrent flow in the 'path having this lower reactance is utilized as the amplied electrical impulse to the exclusionI of the` current in the other path.

2. In a system of the class described comprising two circuits, the second taking energy from the first. said rst circuit having two paths one of which is coupled to said second circuit, -means .for tuningsaid second circuit selectively through 4`a given range of radio frequencies, the two separate paths of said rst circuit comprising imped ance elements so proportioned that the ratio of the current through the said coupled path to the' current in the uncoupled path decreases with increase in the selected frequency, whereby the energy transfer ratio between said circuits will tend to remain constant.

3. In a system of theclass described an amplipaths comprising an inductance element and the w .other vpath*an--inductancean'd a condenser element in serie s,'means for tuning said control-circuit :througha. selected range of frequencies, means for inductively coupling said control circuit with at least onepath of said output circuit, r whereby energy is transferred to said control circuit, said elements lbeing so proportioned :with

rent through said rst named path' to the current through said second named path increases with an increase in frequency, whereby the en- 4 ner having control and output circuits, a pair of separate paths -insaid output circuit, one of said respect to each other thatthe ratio of the cur- .ergy transfer between said output and control cies the current will be relatively small but for circuits will be independent of frequency. lower radio frequencies simultaneously intro- 4. The method of reactively coupling the outduced into the output circuit the current will be put circuit of a high frequency amplifier with relatively high, whereby substantially aconstant 5 another circuit comprising automatically varying energy transfer ratio will be maintained thnough- .5

the current flowing in an interlinking reactive out a given frequency range. y

element so that for relatively high radio frequen- FREDERICK A. KOLSTER. 

